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Nessism wrote: In an earlier post you mentioned measuring the bearing shells in three places and then (presumably) averaging. I think it would be better to take the thickest of your readings because that would show the least wear condition.

Very good point. I'll measure again and take the largest reading.

Warren3200gt wrote: Just a thought, you did use a new ball bearing which is perfectly spherical and not an old worn one? If you measured an old one in several places it would be a different reading and skew your calcs.

Also a good point. I measured the bearing several times and always got the same measurement, but it won't hurt to get a new ball bearing when I remeasure, just to eliminate a possible mistake.

I'd use a 1/4" ball and tape it onto the micrometers mandrel so it doesn't move around. When using the mic don't tighten too much or the ball will dent the babbit on the bearing face and give you a wrong reading. I'd measure each shell and look for the largest reading.

BTW, you can buy those ball adapter thingies for mics. I'm not suggesting you buy this just showing it's a somewhat common tool...www.amazon.com/Starrett-247C-Micrometer-...&sr=1-19&ref=sr_1_19

This is absolutely maddening. I have measured and remeasured these main bearings and I'm completely confident in my measurements. All but one of these measure less than the thickness of the "brown" bearing thickness, and most are significantly less than the that. My oil clearance is right on the money according to the Plastigage.

The average of all 5 upper and lower main bearings (10 measurements total) is .0583", or 1.48082mm.

The measurement range of the "brown" bearings is .0586" - .0588", or, 1.4884mm - 1.4935mm.

I have verified and double verified the zero on my micrometer. How can obviously worn bearings be thicker than new bearings? The only answer I can think of is the thickness listed on the new bearings is either not correct (unlikely) or is measured in some other way, thought I can't imagine how. I'm ready to just say screw it and order the "brown" bearings. The only thing stopping me is those stupid crankshaft and case markings (lack thereof) that say I need the "blue" bearings.

If I ever get this sorted out I'll have to start all over with the rod bearings. Maddening.

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No eBay APP ID and/or Cert ID defined in Kunena configurationNo eBay APP ID and/or Cert ID defined in Kunena configurationThe parts fishe shows that those bearings were used on a lot of different Kawasaki model bikes. Since the bearing situation is so murky I think I'd order up one sample brown bearing and then measure it when it arrives so you can compare to what you have. Or maybe buy some clean used bearings. These may be worth a gamble. I wouldn't be afraid of used as long as they are clean. On my 750 I took bearings from two engines and combined the best samples from both and used them.

To end the mystery once and for all, torque the engine cases together without the crank or bearings and then take them to any sort of engine machinist and politely ask them if they could quickly measure one of the crank journals and one of the bearing bores in the case and lastly one of your bearing shells. They will have the stupid expensive gauges and expertise that will accurately tell you the precise measurements of each, which will tell you what bearing you have and whether there are discrepancies in the case and crank markings. That should give exactly information and piece of mind that you will be buying the correct bearings and that it wont seize up 20 min after you start it.
It would be a shame to waste time, money and destroying a crank only to find out you micrometer was giving you wonky readings.
It might help if you hand them a $20 bill for their time to do it while you wait. Thankfully my machinist measured my bearings for free. ( My case used all blue except for one journal that called for black. But the color had rubbed off the shells and I wanted to make 150% of the thickness before I ordered new ones.)

The pre 1983 kz650's and 750's used a different bearing composition, and through the years they were all sold. So I think Kawasaki started shipping the 83 and on up to the 2005 ninja 550r bearings for the earlier bikes as they fit just fine, but they are made of a different alloy. Oddly enough they changed the composition again for the zr-7's, but they still fit. ( I am using zr-7 connecting rod bearings in my kz750 as they were way cheaper. But again, they have completely different part numbers and color coding system)

Here is excerpt from a 1983 Cycle magazine about the new uni-track gpz750 where it mentions the bearing change.

To measure the crankcase bores properly a three point internal micrometer is useful. A two point bore gauge can be used but there will be more measurement error compared to a three point tool. And a properly calibrated micrometer is needed to measure the crank and bearings, one that can read down to 1/10,000". It's pretty common for a micrometer to be 1/2 a thousands out of calibration, so checking it against a "standard" is suggested as a sanity check before trusting the numbers you get using the tool.

More good advice, and I'm thankful for it. The used bearing idea is a good one and I'll keep it in mind. Yesterday I almost ordered one each of the main bearing colors, and while its not a lot of money it goes against my financial sensibilities. One thing I thought about was my crankshaft journal measurement. According to my measurements my crank journals fall into the range where it should have the "o" marking. By applying that measurement to the chart my bearing requirement would call for a different bearing than the unmarked crank I apparently have. That led to the idea that my case crank journal bore might also measure differently than an unmarked case would measure. The only way to be sure is to measure those bores (as Daftrusty suggested). So yesterday I ordered a set of Lufkin bore gages. I think thats the missing measurement and the one that might solve this mystery. Perhaps my crank and cases should have been marked but weren't.

As for my micrometer I checked it at .000 reading and also used a 1" standard to check it at 1.000" (like Nessism suggested). Its an old Starrett mic (which doesn't mean much I admit) but it does check out as on the money at both ends of its spectrum. I plan to buy a mic that reads to .0001 in the near future. I bid on a Swiss made Brown & Sharpe but the price got higher than I want to pay.

Once I have all of the measurements I'll compare them to the spec. in the manual and see where I'm at. If there's still a question I'll tear down my spare engine and maybe I'll have a useable set there. If not it may be off to Ebay for a used set. One thing is certain though, I'm having fun with this, which is the whole point!

My Lufkin bore gauges arrived and this evening I torqued the engine cases together without the crank bearings. I took three measurements of each of the five crank journal bores and averaged the three readings to get a solid measurement of each journal bore diameter. Number one is 39.0067mm, number two is 39.0025mm, number three is 39.0076mm, number four is 39.0118mm, and number five is 38.9974mm. According to the manual the crankshaft bearing inside diameter range of 39.000 - 39.008mm should have the "o" marking. The average of my five is 39.0052mm, which is smack dab inside that range, which means my crankshaft should have the "o" marking. My crankshaft journal diameter is 35.9993mm, which should have the "1" marking.

Setting the markings (or lack thereof) aside my engine component measurements say I need the "brown" crankshaft bearing size. The only remaining hiccup is my actual bearing thickness measuring less than the smallest bearing thickness. The smallest bearing thickness is 1.490mm, and mine measure 1.4808mm average. To put the number is perspective my main bearings have approximately .0092mm of wear, which converts to .0003" wear. That seems normal to me and the measurements seem to make sense now.

To sum this all up I'm going to order a set of "brown" main bearings with a high level of confidence that these will work in this engine. Thanks to all who have helped. I'll update once I have the bearing in and have a chance to verify with Plastigage.